Diseases of the heart and blood vessels produce more deaths in this country than all other causes of death combined. Why atherosclerosis, (hardening of the arteries) developes is not fully understood; but it is often associated with elevated blood cholesterol levels. Cholesterol is transported by the body in fat-protein complexes called lipoproteins. Recently, population and other studies have shown that one such lipoprotein complex, HDL does not contribute to heart disease but may in fact protect against coronary disease. This knowledge has produced a high demand for measurement of HDL by clinical as well as research laboratories. Present methods are somewhat rudimentary and little information is available about HDL to assess its protective effect. We plan to 1) evaluate current precipitation methods for HDL cholesterol quantitation; 2) to evaluate quality control materials for HDL cholesterol quantitation; 3) to apply the HDL measurement methods to clinical studies; 4) to develop an accurate and precise method for HDL quantitation that is suitable for the clinical laboratory; 5) to assess and optimize the effects of sampling, handling, and storage conditions on the HDL precipitation procedure; 6) to develop a reference procedure for HDL cholesterol separation and quantitation which can be used to assess the specificity of routine separation methods; and 7) to develop methods for convenient separation and quantitation of the HDL subclasses.